I have similar problem. 86 325e, 160K. New plugs, rotor, dist cap, O2 sensor & fuel pump. Car will run fine, then when go to start it up, it too seems like it's running on half the cylinders. Must keep accelerator depressed until engine "clears up." Visible black smoke during this time out the exhaust, then, seems like the little gremlin goes away and all is good. What gives???